function diff = J_n_pp( m, param)
    % calculates J\prime\prime(m) in natural wastage region
    diff = param.J_1*m.^(param.gamma_N_1-2).*param.gamma_N_1.*(param.gamma_N_1-1) ...
            + param.J_2*m.^(param.gamma_N_2-2).*param.gamma_N_2.*(param.gamma_N_2-1);

end